High performance components in aircraft engine turbomachines such as compressor blades, bearings and gears are typically coated with a titanium metal compound such as TiN to improve their wear characteristics and to provide erosion protection. The engine parts are cast or otherwise molded or machined from superalloys, stainless steels or alloy steels and represent very expensive precision components. Removal of the coating from the underlying base metal is necessary if a defect is discovered in the coating and/or for restoring worn components. It is essential to strip the protective coating from the base metal without suffering any detrimental attack to the underlying base metal.
To selectively strip a titanium compound such as TiN from a solid base metal composed of a superalloy, stainless steel or alloy steel without chemically attacking the base metal is particularly difficult when both the base metal and coating have a high corrosion resistance characteristic. Stripping is even more difficult when the corrosion resistance of the coating is equal to or greater than the corrosion resistance of the substrate.
Although, stripping solutions containing hydrogen peroxide are known there is no known aqueous based stripping solution using hydrogen peroxide which will permit the removal of a coating of a titanium compound from a solid base metal composed of a superalloy, stainless steel or alloy steel without causing detrimental attack to the underlying base metal. A chemical stripping solution comprising hydrogen peroxide is described in U.S. Pat. Nos. 4,554,049, 4,410,396 and 4,545,918 respectively. The stripping solutions disclosed in these patents are either unable to strip compounds of titanium from base metals composed of superalloys stainless steels and alloy steels or will actively attack both the titanium compound coating and the base metal.